This invention relates generally to lubricants and more particularly has reference to lubricants containing a dispersion of solid lubricant particles.
Pertinent U.S. and foreign patents are found in Class 252, subclasses 60 and 58 and in Class 585, subclass 12 of the Official Classification of Patents in the U.S. Patent and Trademark Office. Examples of pertinent patents are U.S. Pat. Nos. 2,510,112, 3,159,557, 3,194,762, 3,314,889, 3,432,431, 3,493,513, 3,505,229, 3,536,624, 3,640,859, 3,723,317, 3,933,656, 4,029,870, 4,127,491, 4,224,173.
U.S. Pat. No. 4,224,173 describes an eight step method for making lubricant oil containing polytetrafluoroethylene particles and a fluorochemical surfactant.
U.S. Pat. No. 2,510,112 describes an aqueous dispersion of colloidal polymerized polytetrafluoroethylene in a fluorinated hydrocarbon oil.
U.S. Pat. No. 3,194,762 describes a product having resin particles suspended in an oil base.
U.S. Pat. Nos. 3,159,557, 3,432,431, 3,493,513, 3,505,229, 3,630,901, and 3,640,859 describe greases containing polytetrafluoroethylene particles.
U.S. Pat. No. 3,723,317 describes a grease wherein triazene is combined with polytetrafluoroethylene to thicken a fluorinated polyether base oil.
U.S. Pat. No. 4,029,870 describes unsintered polytetrafluoroethylene which has been irradiated.
U.S. Pat. No. 3,933,656 describes sub-micron polytetrafluoroethylene particles.
U.S. Pat. No. 4,127,491 describes an aqueous dispersion of polytetrafluoroethylene particles.
The benefits of solid particle lubricant additives have been recognized for some time. Tests indicate varying but consistent improvements in engine efficiency through the use of molybdenum disulfide and graphite. The effects of solid particles as a cushion between sliding metal parts having been established, the natural tendency is to develop improved or advanced products. Polytetrafluoroethylene has been introduced as a solid particle additive that exhibits the same cushioning effects as molybdenum disulfate and graphite, but with the advantage of being a cleaner material to work with and a better or lower friction lubricant.
However, there are several problems associated with the use of polytetrafluoroethylene particle additives.
The preparation of a stable dispersion through chemical stabilization of polytetrafluoroethylene is a complex and exacting science. One such stabilization technique is described in U.S. Pat. No. 4,127,491.
Moreover, the dispersion achieved by the chemical stabilization method is short-lived. Upon standing for short periods of time, the particles settle and develop what could be called a "hard settle", i.e., the particles cannot be redispersed.
Added to the "hard settling" problem are the in-service problems of short-lived effectiveness. The apparent problem with dispersions achieved by the chemical stabilization method is that the surface active materials and film forming polymers become ineffective after a brief period of use.